The present invention relates in general to vehicle air filters and to the overall theory of air filtration for an internal combustion engine. More specifically the present invention relates to high-efficiency air filters, air filters which are incorporated into the engine block and the use of a combination of filters in a filtering network to provide cleaner intake air to the engine.
Traditionally, automotive air filters have been designed as separate, add-on components to the engine air intake system. One result or this design philosophy has been the evolution of cannister-type air filters. However, these air filters are bulky and must be utilized in combination with external connecting conduits involving several assembly steps as well as several components. The outcome is typically an air filter installation which is prone to leakage. Another potential problem is that these bulky, cannister filters may admit dust to the engine when the air intake system is being service. A still further potential problem for the manufacturer of the air filter is the integrity of the installation which will be performed by the purchaser--OEM. Since system responsibility rests with the OEM, the quality of each installation can vary and there is no fixed or standard quality level.
The present invention addresses these concerns in a number of ways by the filter designs and filter system arrangements which are disclosed and described herein. The present invention provides a high-efficiency precleaner filter which may be arranged in alternative forms. Also included as part of the present invention is a barrier filter which is incorporated directly into the engine block (intake manifold) in order to trap any remaining dust which is not trapped by whatever filter arrangement may be installed upstream from the engine block. This integrated filter also helps to protect the engine from dust in any original or replacement air intake plumbing or components.
Part of the theory embodied in the present invention as it relates to diesel engines can be explained in the following manner. Since diesel engines are turbocharged, the air on the pressure side of the turbocharger has a greater density, and thus a smaller filter can be used to achieve the same dust-holding capacity. It is a well established fact that reducing the "face velocity" of flow through a given area of filtering medium allows a higher dust holding capacity to be realized. The increased air density in effect reduces the velocity of flow through the medium and provides that benefit. Secondly, since the thermodynamic "work" associated with pumping a gas volume (assumed incompressible) across a restriction is equal to the volume times the restriction, then the maximum allowable restriction (termination restriction level) for a pressure side integrated air filter is larger since the volume of gas is smaller due to increased density. Specifically, assuming equal air temperatures, for equal "work" and hence engine performance, the termination restriction for a pressure side integrated air filter is equal to the conventional "upstream of turbo" termination restriction level (usually 25 in H.sub.2 O for turbo diesels) multiplied by the turbo boost ratio (usually around 2.5 for turbo diesels). Simply put, a filter on the pressure side of the turbocharger can be "plugged" to a higher degree since the pumping energy remains lower due to the lower volume flow. Consequently, a filter placed downstream of a turbocharger can hold more dust than a naturally-aspirated filter with the same pressure drop. Combining with filter with a suitable precleaner will significantly lengthen the service interval for the engine. Another advantage of an integrated filter system, such as that disclosed herein, is that it allows the engine manufacturer to carefully control the air filtration quality and this is expected to reduce warranty claims directed to dust which is ingested by the engine during servicing.
The integrated air filter which is housed in the engine block (intake manifold) requires very little space due to its geometry and does not require any housing. When this integrated air filter is used as a primary air filter, an upstream, inertial precleaner (or similar precleaner) is needed to protect the turbocharger. However, this integrated air filter could simply be used as a safety filter without regard to what type of upstream filtration system is in place. In this approach, this "safety" filter would provide advantages to the end-user in terms of fail-safe engine protection.
Improvement efforts for air filters and air filtration systems have been ongoing for a number of years. Some of these efforts have resulted in issued United States patents. A representative sample of such patents is listed below and while each may possess certain elements of novelty, as its time of issue, none are believed to be particularly close to the teachings of the present invention:
______________________________________ U.S. Pat. No. Patentee Issue Date ______________________________________ 3,884,658 Roach May 20, 1975 4,204,848 Schulmeister et al. May 27, 1980 4,347,068 Cooper Aug. 31, 1982 4,373,940 Petersen Feb. 15, 1983 4,482,365 Roach Nov. 13, 1984 4,673,503 Fujimoto Jun. 16, 1987 4,702,756 Yajima Oct. 27, 1987 5,125,940 Stanhope et al. Jun. 30, 1992 ______________________________________